Fish gill fossils gnaw at ideas of jaw evolution

This three-dimensional reconstruction shows the skull of the sharklike Ozarcus mapesae. The braincase appears in light gray, the jaw in red, the gill arches in yellow and the horseshoe-shaped hyoid bone in blue.

Bony fishes, not modern sharks, may provide a better understanding of the earliest jawed animals and the evolution of the jaw itself.

Fossils of a 325-million-year-old sharklike creature show that the newly named Ozarcus mapesae had a gill structure more similar to bony fishes, such as sunfish, than to modern sharks, rays and other non-bony fishes. Described April 16 in Nature, the bones also appear to counter the idea that modern sharks are living relics of earlier times and suggest that the fish group acquired bone structures and other features that may have evolved with time.